The present invention relates to a bond pad having reduced capacitance which is useful in fabricating integrated circuit and communications devices and to a method of reducing the capacitance of a bond pad.
Communications systems typically include a variety of devices (e.g., integrated circuits, light sources, photodetectors, switches, optical fibers, amplifiers, filters, and so forth). Communications systems are useful for transmitting information, such as information relayed by optical signals, over long distances at high speeds. As communications systems become more advanced, signals are being transmitted at higher frequencies. However, high-speed devices are plagued by parasitic capacitances that can be detrimental to the performance. A major contributor to parasitic capacitance is that associated with bond pads.
Bond pads find many applications in connecting integrated circuit devices and components of communications systems. See, e.g., U.S. Pat. No. 5,976,964 to Ball, xe2x80x9cMethod of Improving Interconnect of Semiconductor Device by Utilizing a Flattened Ball Bondxe2x80x9d; U.S. Pat. No. 5,587,336 to Wang et al., xe2x80x9cBump Formation on Yielded Semiconductor Dies,xe2x80x9d and U.S. Pat. No. 5,577,944 to Taylor, xe2x80x9cInterconnect for Use in Flat Panel Display,xe2x80x9d incorporated herein. A top view of a communications device including a typical bond pad is schematically illustrated in FIG. 1A, with a side view shown in FIG. 1B. The bond pad 10, which typically is fabricated with gold (Au), is disposed on a substrate 8 with an insulating layer 11 therebetween (hidden from view in FIG. 1A). The insulating layer 11 may be comprised, for example, of SiO2 or semi-insulating InP. The bond pad 10 is connected to the device 12 by an interconnect 13 which may take various dimensions. For example, the interconnect may be fabricated with the same material as the bond pad, comprise a bond wire, or be fabricated with other materials as known in the field.
A large bond pad is disadvantageous with regard to the system capacitance, but is used to achieve good adhesion of the pad to the insulating layer and interconnect. The interconnect does not require a large surface area to achieve a good electrical connection. As may be appreciated, it would be advantageous to provide a bond pad that maintains the advantages of achieving good adhesion and yet has less parasitic capacitance.
Summarily described, the invention embraces a bond pad structure that has a reduced capacitance and yet maintains good adhesion and electrical connection properties. The bond pad is adapted for coupling a device with an interconnect. The bond pad is disposed within a select pad area. It includes a two-phased region of air and conductive bonding material within the select pad area and a ribbon of conductive material within the select pad area overlapping the two-phased region. An interconnect is coupled to the ribbon and to the device. In a preferred embodiment, the regions of air and bonding material define a mesh geometry. Including air within the bond pad structure reduces the capacitance of the device, while the surface area of the bonding pad is maintained to at least substantially retain the adhesive properties of the pad. The ribbon of conductive material maintains good electrical properties for the bond pad.